Road Bridge Saved From Decay Thanks To Sika’s Sacrificial Anodes

When it comes to the management and maintenance of major concrete structures such as roads and bridges, preventative measures are preferable to repair works – saving substantial costs and time to complete, thereby minimising disruption to users.

This was the case for Almond Valley Bridge, a twin-deck structure located in Livingston near Edinburgh. The 900m-long bridge, which contains three traffic lanes within each deck, was subject to an independent 10-year survey to detect linear polarisation within the reinforced concrete.

Tests revealed high levels of chloride which, if left untreated, would have resulted in corrosion sites on the steel rebar. This would have led to the concrete surface becoming cracked and spalled, thus affecting the bridge’s structural integrity. Contractors Chemcem Scotland, on behalf of West Lothian Council, required a proven management system which offered long-term corrosion prevention, eliminating the need for costly, time-consuming repairs.

Work on the Almond Valley Bridge corrosion prevention project began in July 2017. Time was of the essence to stop further corrosion, the effects of which would have become visible without treatment and would require extensive concrete break-out & replacement if a traditional approach was adapted.

This would have involved taking the concrete back to the rebar including removing structurally sound chloride contaminated concrete, then replacing with a suitable repair mortar. To provide a more sustainable and less invasive approach, to control corrosion, Zinc anodes were included in the repair areas and in the remaining structurally sound chloride contaminated concrete. West Lothian Council recognised the combination of Sika Galvashield XP and CC Anodes as the perfect preventative measure; a simple and easy-to-install solution which negated the future need for a costly bridge repair and closure scheme to therefore benefit the client, the tax paying public and the environment.

The Sika solution

Sika Galvashield sacrificial anodes are quickly and easily installed into concrete to control corrosion activity and prevent the new formation of corrosion sites on reinforced concrete structures. Anodes are available in a range of shapes and sizes and comprised of a specially-formulated precast cementitious mortar which surrounds and activates its sacrificial zinc core.

When correctly installed the zinc anode corrodes preferentially to the surrounding steel, providing galvanic corrosion prevention and control to the adjacent reinforcement. Sika Galvashield XP and CC anodes offer corrosion control for a range of reinforced concrete buildings including columns and beams, piers and marine structures, car parks and bridge decks and post-tensioning anchors.

For the Almond Valley Bridge project, a total of 2,800 anodes were installed. The bridge’s height, approximately 40 metres from the ground, presented on-site teams with a potentially challenging repairs programme. For the installation of the anodes, contractors occupied two cradles which were hung from the side of the bridge.

The affected carriageway remained closed whilst installation of the corrosion management was carried out, hence the need for a rapid, easy-to-install solution. With CC anodes there is no requirement to break- out the chloride contaminated concrete, which creates dust and debris being released into the atmosphere plus reduces the workers time being exposed to percussive tools which can cause hand transmitted vibration health issues. The process simply involves drilling a small hole and inserting the anode into the concrete.

A small amount of mortar is used to cover the hole. The Sika Galvashield CC anodes were installed at 400mm intervals along the bridge’s soffits and columns.

Alasdair Beaton, Managing Director of Chemcem Scotland, said: “The CC anode system was ideal for the Almond Valley project, as we needed to prevent further corrosive activity within the concrete whilst minimizing carriageway closure times and disruption to motorists.

“The system’s easy-to-install properties were a real benefit to our on-site teams who were working at height. It also meant we were able to keep project costs to a minimum. Thanks to Sika Galvashield anodes, we were able to limit the time spent on site; so much so, we completed the repairs programme eight days ahead of the eight-week deadline. This really is a superb system – it’s good for the environment and extends the life of the structure without the need for a costly maintenance or repair programme.”

Sika Galvashield anodes feature a range of benefits which make them ideal as a corrosion prohibitor in concrete structures.

Protecting local areas that are chloride contaminated, but sound, thereby reducing concrete breakout.

Effectiveness in chloride-contaminated and carbonated concrete for use in both conventionally reinforced and pre-stressed or post-tensioned concrete.

Quick and easy installation.

Low maintenance, as the anode system eliminated the requirement for an external power source or system monitoring.

Anode performance can be easily monitored if required.

The system offers a 10 to 20-year service life reduces the need for future repairs

The easy-to-install Sika Galvashield anodes system not only ensured the preventative works programme was completed eight days ahead of the agreed two-month timeframe, it will provide long-term protection against potential damage caused by corrosion, ensuring this fine structure will continue to provide daily access for thousands of vehicles for many years to come.